Overload release mechanism



April 24, 1951 C HALL Re. 23,361 1 OVERLOAD RELEASE MECHANISM Original Filed May 17, 1945 IN VEN TOR.

Garizbe 014 Reissued Apr. 24, 1951 OVERLOAD RELEASE MECHANISM Cortice H. Hall, Jackson, Mich., assignorto The Timken-Detroit Axle Company, Detroit, Mich., a corporation of Ohio Original No. 2,425,736, dated August 19, 1947, Se-

rial No. 594,323, May 17, 1945. Application for reissue February 28, 1949, Serial No. 78,830

Matter enclosed in heavy brackets appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue.

3 Claims.

This invention relates to overload release mechanism for disconnecting a rotating driving member from a motor driven thereby when the transmitted torque exceeds a predetermined amount and is particularly concerned with 'such overload release mechanism for interrupting the drive of a material feed shaft by a motor or the like, as in a mechanical coal stoker, where the feed may become clogged or blocked by large pieces of coal or solid foreign material.

Various forms of torque responsive overload release devices have been suggested for use in web feeding machinery, coal stokers and other apparatus, but few if any of these devices are embodied in commercially produced coal stokers, the function being accomplished usually by con ventional shear pins which break when the torque exceeds a certain amount. The difficulty with such shear pins is that, although they perform the drive breaking function adequately when properly designed, the device must usually be partially dismantled in order to replace them and this requires time and labor.

Various types of resettable overload release devices have also been proposed but these are mainly relatively complicated or of such other practically objectionable nature that their use has not become general.

In the present invention I provide a mechanically simple overload'release mechanism which breaks the driving connection cleanly and very rapidly when subjected to a predetermined torsional overload and which is easy to reset when the cause of the overload condition has been remedied. My mechanism is such that it may be carriedon a conventional part of the usual drive for a stoker feed or the like, so that it may be adapted into an existing installation with minimum conversion.

With the above in mind, it is a major object of my, invention to provide a novel, mechanically simple and inexpensive and reliably operable overload release mechanism adapted to interrupt a drive connection between a rotatable driving member and a driven member when the torque transmitted thereby exceeds a predetermined amount.

A further object of the invention is to provide a novel extremely sensitive and rapidly acting overload release mechanism operable to interrupt a drive connection in response to minimum torsional overload.

A further object of the invention is to provide a novel cam and resiliently biased lever assembly adapted for positively transmitting a driving torque and adapted to break the drive when a predetermined torque is exceeded, and which is easily and conveniently resettable without dismantling any of the assembly and associated apparatus.

A further object of the invention is to provide a simple torsional overload release mechanism bodiment of my invention mounted on a drive pulley, illustrative of a rotary driving member, for rotating a shaft such as the feed drive shaft of, a coal stoker conveyor, illustrative of the driven member in the assembly, and illustrating the parts in set relation where the drive and driven members are positioned for transmission of torque through the mechanism;

Figure 2 is an end elevation of the mechanism of Figure 1 illustrating the position of the parts when drive has been interrupted, as when the mechanism has been overloaded by restraining rotation of the driven shaft;

Figure 3 is a side elevation, partly in section, illustrating constructional details of the mechanism of Figure 1 as mounted on the drive pulley; and

Figure 4 is a fragmentary sectional view taken substantially alongline 4-4 in Figure 1 illustrating the connection between the drive arm and the release rocker bar in the mechanism of Figure 1. r

In its preferred embodiment the invention is especially adapted for interrupting the drive between a power plant such as an electric motor and a rotatable shaft driving a coal stoker conveyor worm such as may be subject to restraining or blocking of rotation as when an oversized piece of coal, stone or iron may become accidentally blocked therein. It will be understood that the invention is not so limited, however, and can be applied to any apparatus wherein a similar overload release problem is presented.

In the illustrated embodiment of the invention, the driving member of the mechanism is a grooved pulley ll adapted to be continuously rotated by a suitable electric motor (not shown) to which it is coupled by a driving belt I2, the disposition of belt I2 in one or the other of the easel different diameter grooves of pulley I I determining the speed of rotation of the pulley. This .pulley may be substantially of the same structure as the usual pulley which is employed in a conventional type stoker worm drive, and all of the overload release mechanism of the invention is carried by the pulley, whereby a novel pulley and associated release mechanism of the invention may be simply substituted for the standard pulley in a conventional stoker feed mechanism. No other alteration in the stoker feed is necessary. The device may be installed by unskilled workmen, and it takes up no more space than a standard pulley.

The driven member in the illustrated embodiment of the invention is the rotatable shaft I3 which may be the driving shaft for the worm of a conventional stoker or may drive the coal feed mechanism through a suitable drive reduction transmission gearing. In any event, the mechanism operated by shaft i3 may be of any conventional construction and need not be further described. It is only important to understand that it is of such character that it may besubject to unpredictable conditions which slow rotation of shaft 13' relative to the pulley so as to produce a torque overload in the mechanism' and thereby actuate the drive interrupting mechanism later described.

- Pulley II is formed-With a central hub l4 lined with a fixed bushing sleeve I5 surrounding the end of shaft l3 with a bearing fit, As illustrated in Figure 3, the outer end of shaft l3 projects a small amount beyond the outer end of hub I4 and bushing [5' which terminates at the end of the hub, and has fixedly secured thereto, as by set screw IT, a collar l5 which is annular and-mainly cylindrical with a radially disposed fiat stop or thrust face I 8 formed on an integralv external projection thereon. As illustrated. this projection is mainly fiat-surfaced to provide a suitable entry face for screw IT. Collar I6 is thus rigid with shaft i3 and comprises a drive connecting element between the shaft andthe pulley.

As illustrated best at Figure 3, pulley H is somewhat recessed on its outer side at 13 and provided with'an integralboss formation 23 on which is rigidly mounted, as by threaded fit with the carrier boss 20, a cylindrical pin 2| which extends outwardly parallel to the axis of shaft [3.

Pin 2| functions as a stationary pivot for a drivev member 22 comprising a bell crank lever formed with intermediate boss portion 23 and two armsdisposed at an obtuse angle projecting oppositely from said boss. Boss 23 is rotatably mounted on pin 2| and lever 22 is held against axial displacement thereon as by a suitable washer and fastener assembly 24. Member 22 comprises a pair of laterally spaced plates 25 and 26 rigid with opposite sides of hub 23 and carrying between their adjacent lower ends a cylindrical roller 21 freely rotatable about a pin 28 fixed at opposite ends to. plates 25 and 25, as

by peening over.

The upper arm of member 22 is at an obtuse angle to the arm. carrying roller 21 and similarly carries a roller 23 freely rotatable about a pin 3| aflixed at opposite ends to plates 25 and 25. Thus drive member 22 is freely pivoted intermediate its ends about pivot pin 2|, and provided with freely rotatable anti-friction rollers 21 and 29 at its opposite angularly disposed ends.

Roller 29 is adapted to seat in bearing line contact with the radial flat stop face [8 of cam 4 collar [6 when the parts are set for driving of the shaft I3 by pulley II, as in the position illustrated in Figure 1. Face l8 must be of sufficient radial depth to permit roller 29 to be se curely seated against face l8.

Radially spaced from hub [4, a pivot pin 32 is-mounted on pulley ll similarly to pin 2| to serve as a stationary pivot upon which is rock ably mounted substantially midway between its ends a fiat-sided, relatively narrow release rocker bar or lever 33. Near one end, bar 33 is formed with an elongated aperture 30 having a flat upper face 34 and longitudinally space arcuate recesses 35 and 36 opposite face 34. intermediate recesses 35- and 36, the wall of aperture 30 opposite face 34 is formed with an internal projection 31 provided with a short flat face 37' preferably parallel to face 34 and an inclined (jamming face 38 extending from face 3'! to merge with the arcuate wall of recess 36. The lower arm of drive member 22 embraces bar 33, plates 25 and 26 extending on opposite sides thereof and roller 21 being disposed in aperture 30 in either of recesses 35 or 3B. Sufiicient space is provided between faces 34 and 31' to permit passage of roller 21 between recess 35 and recess 36 during the below described operation.

Release rocker bar 33 is resiliently biased in a clockwise direction in Figures 1 and 2, as by a release spring 40 extending between suitable spring retainer collars 4| and 42 provided on cylindrical spring guide pins 43 and 44 mounted respectively on bar 33 and an anchor block 45 having a cylindrical part 46 journalled on pulley Ii. Spring guide pin 44 is formed at its end remote from release spring 40 with a threaded portion 4'! rotatably engaged with pivoted block 45, and a nut 43 mounted on said threaded portion 41 beyond-pivoted block 43 is adjustable for determining the projection of pin 44 from block 45, whereby adjustment of nut 48 effects an adjustment of the compression of release spring 43 and thereby controls the value of the torque load which may be transmitted by the mechanism prior to interruption of the drive. 7

In operation, the drive member 22 and bar 33 are usually set in the drive position illustrated in Figure 1, wherein roller 29is disposed against radial face It of the cam collar and roller 21 is disposed in recess 35, the parts being maintained in this position by the expansive force of spring 43 which reacts against the anchor at 45. Spring 40 is of sufiicient strength to maintain roller 21' in recess 35 and roller 29 against face l8 during normal drive. The cylindrical surface of collar It at the base of stop face [8 serves as a stop limiting clockwise rotation of drive member or lever 22 by spring 4|].

With the parts in the set position of Figure 1, motor? driven rotation of pulley I I positively rotates shaft [3, the drive force being transmitted through lever 22 and roller 29 between pin 2| and face 18. Pin 21 is located on the driving member in such a. position that the line of action of the resultant thrust force of the lever 22 against the face 18 is substantially that between the ares of roller 29 and pin 21-. The line between the centers of pin 2| and roller 21, representing the direction of the drive force, is at an obtuse angle a. with respect to face 18 so that were it not for spring 40 and bar 33, action of the drive force would simply cause roller 29 to travel radially outwardly on: face I8- andimmediately break the drive connection. However, the.

55 urge lever 22 clockwise compensates for such tendency of the drive force to rock lever 22 counterclockwise during normal drive, and when there is no obstruction to rotation of shaft 13 beyond the normal inertia of the coal or other material being fed. Thus the absolute force of spring 49 must be correlated to the angle a.

Suppose now that rotation of shaft i3 becomes restrained or blocked, as in the case of a coal stoker where an oversized piece of coal or a stone becomes lodged between the worm and conveyor tube. Shaft 12 slows relative to pulley l l and now resists rotation more than in normal feed drive, and more torque is needed to continue to rotate it with pulley Ii. Since, due to the angularity of the drive force and face !8, a certain component or proportion of the drive force always tends to rock lever 22 away from cam face l8, it is apparent that an increase in the driving torque will proportionately increase the force tending to rock lever 22 counterclockwise. As soon as the drive torque increases a predetermined amount, therefore, the increased component of force tending to rock lever 22 counterclockwise overcomes the compensative force of the resilient latch comprising spring 40 and lever 33, which latter force remains unchanged, and lever 22 is rocked counterclockwise and roller 29 is cammed radially along and beyond face i8 to break the drive connection so that pulley ll rotates freely with respect to shaft I3.

Counterclockwise rocking of lever 22 under the influence of the increased drive force results in roller 21 riding over projection 37 [and] to coact ith cam surface 38 of rocker bar 33, which is resiliently biased by spring 40, to positively shift lever 22 by cam action to its disengaged position after the initial nnseating from recess 35, roller 27 becoming lodged in recess 35 where it is maintained or latched by the action of spring 49 so as to positively retain lever 22 out of drive contact with cam collar Hi. This position of the parts is illustrated in Figure 2, a slight rocking of lever 33 against the action of spring 40 permitting the shift of roller 21 between recesses 35 and 36.

The above action takes place very speedily particularly because of the substantially frictionless connection between roller 29 and radial face 18, and between roller 21 and bar 33. Due to these substantially frictionless engagements it will be seen that the entire mechanism. is very sensitive in operation and very speedily shifts between the positions shown in Figures 1 and 2 whereby the drive is automatically and instancously disconnected almost the moment that a torque overload condition is attained. This trigger-like action is of great value in preventing damage to the apparatus.

The use of compression spring as at 40 to continually urge the parts together provides an extremely steady and positive spring pressure control which is not available in many prior devices utilizing tension springs for similar purpose, and the sensitive adjustment afforded by rotation of nut 48 enables the spring to be adjusted through an appreciable range of torsion trip values. This is a very sensitive and reproducible control of the trip value of the mechanism which may also be used to compensate for wear in the parts, and is a very important feature of the invention.

After the obstruction has been taken away, the parts may be set into the position of Figure 1 simply by manually pushing downwardly on the upper part of lever 22 so that roller 29 becomes disposed behind stop face I8, spring 43 permitting the slight rocking movement of bar 33 necessary to allow roller 21 to pass from recess 36 over projection 31 and into recess 35 and camming face 38 facilitating that return movement of roller 21. Spring ill holds the parts in the reset position. The apparatus may thus be reset for immediate use without special equipment or tools and in a minimum time.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States Letters Patent is:

1. In an overload release mechanism, a drive member and a driven member adapted to be rotated together, in drive torque transmitting relation and to be separated to interrupt said drive, one of said members have a flat radial thrust face, a drive transmission lever [armlpivoted on the other of said members having a roller adapted to bear on said face when said members are in drive transmitting relation and a resiliently biased rocker bar pivoted on said other member formed with spaced recesses interconnected by a cam surface, and another roller on said drive tnansmitting lever [arm] adapted to seat in either of said recesses whereby said drive tnansmis sion lever is positively shifted from its drive to its non-drive position by the resiliently biased rocker bar when the second of said rollers has been unseated due to an overload.

[2. In a torsional overload release mechanism embodying rotatable drive and driven members, a drive transmission lever pivoted on one of said members, cooperating separable drive surfaces on said other member and one end of said lever, and a pivoted resilient latch element for said lever mounted on said one member operably connected to the other end of said lever and adapted to hold said lever either in operative drive transmitting contact with said other member or in a position where said surfaces are separated and the drive is interrupted] [3. In a torsional overload release device wherein rotatable drive and driven members are connected by trip mechanism, a generally radial thrust face rigid with said driven member, a drive lever pivoted intermediate its ends on said drive member and adapted at one end for abutting contact with said thrust face, a rocker lever pivoted on said drive member and operatively coupled to the other end of said drive lever, and a compression spring on said drive member acting on and through said rocker lever for maintaining said drive lever either in abutting contact with said face whereby said drive member rotates the driven member or out of engagement with said face whereby the driven member is not rotated by the drive member] [4. In a device defined in claim 3, wherein said drive lever has substantially frictionless roller contact with said stop face and said rocker lever for increasing the sensitivity of said device to [5; In a torsional overload release" mefehar iism adapted toreleafibiy"interconriecit rotatable drive arid driven' memb'ers a drive transmission lever biv'oted ori one of Said membere and adapted to be operativeljy 'c'orme'et ed to the other of said members a pivoted latch bar on said. one memljer f armed with sba'c'ed reeesse alternatively engageable with a; part oh said levergand resiliefit means acting on said latch bar to releasably latch said lever against pivotal movement when said part is disposed in either of said recesses] [6; in the mechanism defined inclaim 5; said res'ilierit means eoihprising an adjustable strength compression spring] I [7: In the mechanism defined in Claim 5, a rockabl e' ahehor on said 'orie member, and a compiession spring between said anchor and said men barn] 8. In ator-io'nal oi erload release mechanism; rotatabl'drive and driven members, a [generally] radial flat thrust face on one member, a latch bar pivoted onthe other member a-i'id'for xried Spaced recesses; a lever pivoted 011 s 'aid oc member; two rol-lers on said lever respet adapted to engage said 'fae e' me either of 'sal'd recesses, (ind a spr'ifig actiiig on vSaid latfih bar for bermitting moiienient or said" assLoeiatd r011- er between said recesses and releasabljr fibldii'i'g said lever agaiiist pivotal movement with theas sociatedroller disposedifieither of said recesses said lever being pivoted at such a p'osition o'ri Said drive member that the line or action of the thrut force 0) the lever agjdiiti Said thrtlstflice 58' 51th stantially that between the axes of said thrust face engaging roller and the lever pivot.

[9. In an overload release meehariis'm; ro'tat able drive and d'rlivii me'm'bers; a b'll-craiik 51votally mounted on one of saidmeiflbrs' with 'oii'e end separably drivecontiebted to aid-otlier ifiifi a a r f i' B ,e n vbb fl'l wh 011 i on'm'" her coupled to the other end of said bell drank. H p

10. I11; lam beerltma. release mechanism, 1a drive mem er 'aflda dririn member adapted to be Totiztd together in drive torque transmitting relation end t6 Separated to interrupt said drive, ojte of said drz'fue m embers having a. flat radial thrust face, name trans mission lever pivoted on the other of said members hapi'n e roller adapted to be'cir on solid fa'c'e when said members are d 13%? tdfismitting r'elation, artd a resiliently biz'r pivoted m said other member I paced recesses interconnected by a "c'aflrisu'rface and another roller 0% said drioe trqns'rrufttifig lever adapted to seat in either of said masses; saie lever b ing pivoted at such a po'sitio'rt on said member that the line of action or the thrust {0 e of the leverdgalnst said thrust f'c iee i5 silli'stahtid'llfy' that between the axes of .5211'tl thrust ja'c'e engaging roller mid the lever mat.

CORTICE' H. HALL.

REFERENCES CITED foilofi rring references are of record in the file of this patent or the original patent:

UNI'T'EE ST-A'IES PATENTS Germany Mar. 23, 1909 

